The present invention relates to an image-forming apparatus such as a copy apparatus or a printer and to a method for detecting a developer amount therein.
Generally, in an image-forming apparatus using an electrophotography method, a toner replenishing unit is attached to a developing device thereof to replenish into the developing device an amount of toner correspondent to the amount of toner consumed in developing, and a toner detecting means is arranged at the toner replenishing unit to detect a toner empty state in the unit.
In the construction, the toner empty state is detected to inform a timing for replenishing toner. Therefore, generally, the detecting means detects a toner complete empty state where toner completely is not left in the unit, but a state where some of toner are left in the unit, that is, a so-called near empty state. Therefore, in the near empty state detected, a considerable amount of the toner is left in the unit. See Japanese Laid-open Patent Publication No. 60-128469.
There is such a type of copy apparatus that the developing device is detachably arranged at the body of the copy apparatus and the device attached to the body is removed therefrom to discard the device when the toner therein is consumed and instead of it, to attach a new developing device filled with toner to the body. In the apparatus, however, it is desired that the detecting means detects a state where the unit is more completely emptied.
Japanese Examined Patent Publication No. 59-46391 discloses that a toner empty detecting sensor is arranged at the bottom of a toner hopper to detect an approximately toner complete empty state. In this method, however, for example, when toner is offset in the hopper or when toner is formed in a bridge configuration at the detecting portion in the hopper, it is possible that the empty state is detected by the sensor by mistake though the toner is left in the housing.